Process of making organic esters of cellulose



Patented June 11, 1929.

UNITED mm. cLAnxE AND CARL .1. mum, on ROCHESTER, NEW roux, AssIGNons TEASTMAN. KODAK COMPANY, or ROCHESTER,-1\TEW YORK, A CORPORATION on NEWYORK.

No Drawing.

This invention relates to processes of making organic esters ofcellulose. One Object of our invention is to pronide an inexpensive andsimple process in which we can 5 utilize satisfactorily forms ofcellulose which have proven difficult to esterify. Another object is toprovide a process in which the cellulosic material is brought intosuch acondition that it will rapidly and uniformly esterify in the knownreaction mixtures, such asthose cutomarily employed for making celluloseacetate, for example. Still another object is to retreat the cellulosicmaterial before esteri cation in a mercerizing bath and then rovide anauxiliary pretreatment which Wlll conserve the good effects of themercerization and yet avoid the resistance to esterification, whichordinarily follows the mercerization process. A further object is toprovide a process in which the cellulosic material is especiallyprepared for esterification and may be dried and stored beforeesterification, without impairing its good qualities. A still furtherobject is to provide a process of making the esters in which neither thepretreating nor the esterification causes any serious moleculardegradation, as is evidenced by the qualities of films made therefrom.Other objects will hereinafter appear.

I It has been generally customary to make cellulosic organic esters,especially cellulose acetate for the manufacture of films, from purifiedcotton of good grade and length. Clearly it is desirable to be able toutilize cheaper sources of' cellulose, such as cotton linters, cottondust, wood pulp, such as bleached sulfite pulp, soda pulp, etc. Furthermore, when utilizing cotton fibers, of

40' good grade, different batches'often behave differently toward theesterification baths. Some of them require longertimes :for

carrying out the reaction, and others show an. unexpectedtendency toleave incompletely esterified fiber particles in the reac tion mixture.It is, therefore, desirable to find a wayto minimize thesepeculiarities.

We have found that the less expensive,

' but more resistant, sources of cellulose may 60.119 used, and moreuniform results: may be rnocnss or MAKING ORGANIC ESTERS or cnnnunosnApplication filed April 23, 1927. Serial No. 186,169.

obtained when employing the high grade celluloses, if the fibers aregiven a mercerizing pretreatment and dehydrated by means fication bathwhile still containing some of H the anhydrous liquid.

While we do not wish to be restricted to any particular theory, sincethe advantages of our process may be obtained irrespective oftheoretical considerations, nevertheless we believe that our processowes much of its eflicacy to the condition which it brings about'in thesurfaces of the cellulose fibers. When such fibers are mercerized, andthe alkali washed out with water, and then the water driven ofi'fromthemby an ordinary slow-drying method in the air, they becomeundesirably resistant to esterification. We believe that this is due tothe formation of a hard, horny surface on the fibers which does notreact readily with the esterification agents, the latter bein unable toreact with the inner parts of the bers while this tough cuticle remains.our dehydrating of the washed mercerized fibers by means of inertorganic anhydrous liquids prevents the formation of this hardened andunreactive outer surface on the fibers. Whether the fibers be then driedby evaporating off the organic liquid, or are We further believe thatstirred into the esterification mixture with some of the liquid stillclingin to them, their surface remams in a soft an reactive conditionwhich permits the esterification agents to react quickly with thesurfaces of the fibers and then quickly with the interiorportionsthereof. v We shall now give several examples of our invention,but it will be understood that The cellulosic material, pre erably inthe fibrous form, is treated with a mercerizing it is notlimited to thedetails thus set forth, except, as indicated in the ap ended claims.

bath of the usual type, such as an aqueous solution of sodium hydroxidof 10% to 40% strength. \Vhile raised temperatures may be employed tohasten the mercerization, we find it ordinarily most convenient to workat room temperature. A bath consisting of and 18% solution of causticsoda in water works well. So long as a useful mercerization of thefibers is obtained, and the latter are not-degraded, the time of themercerizing is relatively unimportant. Using said 18% solution, we haveobtained satisfactory results after one days treatment at roomtemperature, but no harm has appeared after three days treatment in suchsolution, and the time could obviously be prolonged without ill effect.Two days is a good average period. Caustic potash can be similarly used.

After the mercerization, the cellulosic material is washed with water,preferably at room temperature, or the temperature of the ordinarysupply of water, which maybe slightly below room temperature in thewinter, or slightly above it in the summer. The fibers are thus renderedfree from detectable quantities of alkali. lVarm water can be used butis not necessary.

After this washing step, the excess of water is removed from thecellulosic material by pressure, say in a centrifuge, or better, in ahydraulic press. But care is taken that the fibers arenot allowed to drywhile they are still wet withthe wash water.

The fibers are then dehydrated by means of a substantially neutralorganic anhydrous liquid. Ethyl alcohol is a useful dehydrating agent,and may be employed to remove the water from the mercerized and washedfibers in practically the same way that it is often used for removingwater from nitrocellulose fibers which have been previously washed inwater. Methyl, propyl, butyl and amyl alcohols can also be used, but thehigher boiling members of this group offer no marked advantages and .aremore expensive. Acetone has been found to be excel lent as a dehydratingliquid, and ether, either mixed with ethyl or methyl alcohol, or appliedafter methyl or ethyl alcohol, has also been very eflective indehydrating the fibers and leaving them with their surfaces in the bestcondition for the subsequent esterification.

The lower members of the benzene series of hydrocarbons, such as benzol,toluol and xylol are also effective in this respect, ben- 201 beingpreferred. When the latter is employed, the mercerized fibers carryingthe residue of wash water are immersed in the benzol and kept below thesurface of it during the treatment, The bath containing the fibers isthen brought to its boiling point, which is less than that of benzol,owing to the formation of an azeotropic mixture of the latter withwater. Thus the water is carried away by the distillation and themercerized cellulose fibers remain wetted only with benzol andsubstantially free from water.

Of course, the benzol which distills off with the water may be condensedand recovered for further use in the process.

After the cellulosic material is dehydrated, it may be freed from thedehydrating agent by evaporation, the vapors of the dehydrating liquid,such as alcohol, acetone, benzol etc, being condensed and thus recoveredfor future use. Or the cellulosic material may enter an esterifying bathwith the dehydrating agent still in it. As a rule oratb off and recoverthe dehydrating liquid. Then the mercerized cellulosic material may bestored and kept indefinitely, until it is esterified, the surfaces ofthe fibers remaining in their reactive condition.

\Vhen the mercerized cellulosic fibers have been dehydrated with benzol,it may be economical to introduce them, while still wet with benzol,into an esterifying bath of the type in which there is present enoughbenzol, or other non-solvent to produce cellulose esters in the form offibers. Of course, the benzol could be evaporated off before the filmsenter the bath, but that is an extra operation.

Our mercerized and dehydrated cellulosic material may be esterified inany of the usual cellulose esterifying baths in which organic acidanhydrids are employed. Since cellulose acetate is at present the mostwidely used of the organic esters of cellulose, we shall give examplesof the many ecetylating baths which can be used, but it will beunderstoood that the known baths for forming cellulose propionates,butyrates,

stearates and various mixed esters, such as aceto stearates, may beemployed with equal facility. Our pretreatment brings the fibers intoespecially good condition for all of these baths.

In one illustrative embodiment of our invention, long fiber surgicalcotton, properly cleaned, is mercerized in an 18% aqueous caustic sodasolution at room temperature for one day and then washed with water atroom temperature, being finally dehydrated with methyl alcohol, followedby ether. After dehydration the ether is evaporated and 5 parts byweight of the fibers stirred into a bath'comprising 25 parts of aceticacid, 20 parts of acetic anhydrid,'20-parts of chloracetic acid, .1 partof magnesium perchlorate, and. the reaction mixture kept at 60 to C.until it becomes homogeneous and the fibers have all substantiallydissolved. This is ordinarily reached in about three and one-half hours.

This is much less than the time required to acetylatc the samelong-'fibered surgical it is slightly more convenient to evapcottonafter the same mercerizing treatment taln'ng the color much more deeplythan:

where no dehydrating step has taken place,

, but the washed mercerized fibers have been heated at 40 C. to driveofi' the water. Such air-dried mercerized fibers, when immersed in theabove acetylating bath, are in such ahighly resistant condition thatthey are only partially acetylated even aftereight hours, numerouspieces. of fiber being still visible in the reaction mixture. In fact,they require longer for acetylation than do the plain untreatedlong-fibered cotton. Our treatment brings about the acetylation in theshortest time of all and with a greater smoothness of reaction.

In another example of our invention, 10 parts by weight of mercerizedand washed cellulose fibers are soaked in a 10% solution of magnesiumperchlorate and pressed until the weight of the residue is 30 parts.This is then dehydrated by immersing in benzol and distilling ashereinabove described. The 10 parts of dehydrated fibers will thus bethoroughly associated with, 2 parts by weight of magnesium perchlorateand the remaining anhydrous benzol, say 15 parts of the latter. Thismixture is then added to a bath of drid and 160 parts by weight ofcarbontetrachlorid. In place. of the latter any suitable diluent maybesuhstitnted,-say 90 90 parts by weight of benzol or toluol. Thethoroughly mixed reaction mass thus obtained is kept at 50 to .0. untila sample shows that .acetylation is complete. This may take severaldays. The= fibers do not disappear during the reaction. They areseparated from the other ingredientsof the reaction mass in the usualway. I T

Our mercerized and dehydrated fibers may likewisehe used to advantage inany of the esterification processes disclosed in ourcopendingapplications, Serial Nos. 179,176

and 179,177, filed 'March 28, 1928, entitled Processes of making organicesters of 'cellulose containing acyl groups having more than two carbonatoms and Process of making cellulose esters of organic. acids.

' They are very satisfactory-in forming the estersof the fatty acids bythe steps there disclosed.

In the above examples, in place of the long fiber surgical cotton, wecan use less expensive materials, such as cotton linters,

cotton dust, wood pulp, suchfas bleached sulfite pulp, soda pulp, andreverted cellulose, such as rayon fibers from-the viscose orcuprammonium processes, these being'substituted weight for weight in theabove ex-fl I I I I which comprises mercerlzmg cellulose, .in a

amples.

It is also noted that when mercerized cellulosic fibers have beendehydrated and dried by our treatment, their surfaces are in anespecially susceptible condition toward the ordinary dyesusedoncellulose fabrics,

parts by Weight of acetic anhybath, washing out mercerized fibers dried.I I

Having thus described our invention, what we claim as new and desire tosecure by Letters'Patent is:

l. The process of making organic esters of cellulose which comprisesmercerizing cellulosic material with an aqueous alkaline bath,dehydrating it with a substantially anhydrous. neutral organic liquid,and thereafter subjecting the mercerized and dehydrated cellulosicmaterial to an esterifying agent.

2. The process of making organic esters of cellulose whichcomprises'mercerizing the V the action of which have been directly"cellulosic material in an aqueous bath having-an alkalinitycorresponding to from 10' to 40% ofNaOll-ll, Washing out the alkali withwater, roving the water with a. sub

stantially anhydrous and neutral organic liquid which a nonsolvent orthe ester; to be produced, and thereafter treating the mercerized anddehydrated oellulosic "material in an esteri 5;: acid anhydrid.

bath containing a fatty .100 f 4. The pro'ce'ssofmaking organicfesters 1of cellulose which comprises mercerizing the" cellulosic material withan aqueous alkaline l the alkali' fromfthe material with water,removing' the water from 305 I the material with 'a substantiallyanhydrous neutral I volatileorganic liquid. evaporating I I said organicliquid from said material, and

thereafter treat' drated and dried I organic esterifying, agent.

g said merce'rized dolly-- cellulosic material with an.

The process'of making cellulose acetate which comprisesmercerizing'cellulose, inf'a form whichis resistant to esteri'ficationby acetic anhydrid, in an aqueous alkaline bath having an alkalinitycorresponding to from 10 to 40% ofNaOH,' washing out the ali fromfsaidmaterial withfiwater, removing the water from the material with a:substantiall anhydrous -i1eutral-volatile organic liqui and thereafteracetylating' the mercerized,

washed and dehydrated, cellulose an acetylating bath containing aceticanhydrid.

v 6. The process of mg cellulose acetate an alkalinitycorresponding'tofrom 10 to:

40% Nafildh at room temperature, washing.

out the a all from the cellulose Wltll water,

removing the water cerized, washed and from said cellulose withdehydrated cellulose in an acetylatlng bath containing acetic an- 5hydrid.

7. In the process for subsequent treatment the steps of mercerizing withan aqueous alkaline bath, removing of preparing cellulose in chemicalbaths, the raw (2811111016 the alkali, and dehydrating the me'rcerized10 cellulose with a substantially anhydrous neutral organic liquid,whereby drying oil water from the mercerized cellulose in air isavoided. v

Signed at Rochester, New York this 18th 5 day of April, 1927.

HANS T. CLARKE. CARL J. MALM.

